Potential for micromachined actuation of ultra-wide continuously tunable optoelectronic devices

Tailored scaling represents a principle of success that, both in nature and in technology, allows the effectiveness of physical effects to be enhanced. Mutation and selection in nature are imitated in technology, e.g. by model calculation and design. Proper scaling of dimensions in natural photonic crystals and our fabricated artificial 1D photonic crystals (DBRs, distributed Bragg reflectors) enable efficient diffractive interaction in a specific spectral range. For our optical microsystems we illustrate that tailored miniaturization may also increase the mechanical stability and the effectiveness of spectral tuning by thermal and electrostatic actuation, since the relative significance of the fundamental physical forces involved considerably changes with scaling. These basic physical principles are rigorously applied in micromachined 1.55-μm vertical-resonator-based devices. We modeled, implemented and characterized 1.55-μm micromachined optical filters and vertical-cavity surface-emitting laser devices capable of wide, monotonic and kink-free tuning by a single control parameter. Tuning is achieved by mechanical actuation of one or several air-gaps that are part of the vertical resonator including two ultra-highly reflective DBR mirrors of strong refractive index contrast: (i) Δn=2.17 for InP/air-gap DBRs (3.5 periods) using GaInAs sacrificial layers and (ii) Δn=0.5 for Si₃N₄/SiO₂ DBRs (12 periods) with a polymer sacrificial layer to implement the air-cavity. In semiconductor multiple air-gap filters, a continuous tuning of >8% of the absolute wavelength is obtained. Varying the reverse voltage (U=0–5 V) between the membranes (electrostatic actuation), a tuning range of >110 nm was obtained for a large number of devices. The correlation of the wavelength and the applied voltage is accurately reproducible without any hysteresis. In two filters, tuning of 127 and 130 nm was observed for about ΔU=7 V. The extremely wide tuning range and the very small voltage required are record values to the best of our knowledge. For thermally actuated dielectric filters based on polymer sacrificial layers, Δλ/ΔU=-7 nm/V is found. Received: 10 May 2002 / Published online: 8 August 2002     

Vibrational spectroscopic studies and DFT calculations on tribromoacetate and tribromoacetic acid in aqueous solution

Aqueous solutions of sodium tribromoacetate (NaCBr3CO2) and its corresponding acid (CBr3COOH) have been studied using Raman and infrared spectroscopy. The spectra of the species in solution were assigned according to symmetry Cs. Characteristic bands of CBr3CO2-(aq) and the tribromoacetic acid, CBr3COOH(aq), are discussed. For the hydrated anion, the CO2 group, the symmetric CO2 stretching mode at 1332 cm(-1) and the asymmetric stretching mode at 1651 cm(-1) are characteristic while the CO mode at 1730 cm(-1) is characteristic for the spectra of the acid. The stretching mode, νC-C at 912cm(-1) for CBr3CO2-(aq) is 10 cm(-1) lower in the anion compared with that of the acid. These characteristic modes are compared to those in acetate, CH3CO2-(aq). Coupling of the modes are fairly extensive and therefore DFT calculations have been carried out in order to compare the measured spectra with the calculated ones. The geometrical parameters such as bond length and bond angles of the tribromoacetate, and tribromoacetic acid have been obtained and may be compared with the ones published for other acetates and their conjugated acids. CBr3COOH(aq) is a moderately strong acid and the pKa value derived from quantitative Raman measurements is equal to -0.23 at 23°C. The deuterated acid CBr3COOD in heavy water has been measured as well and the assignments were given.     

Zur Ermittlung der günstigsten Integrationszeitkonstanten bei der Durchstrahlungsprüfung

Bei der kontinuierlichen Durchstrahlungsprüfung von Werkstücken werden überwiegend Meßeinrichtungen, bestehend aus ⁶⁰Co-Strahlungsquelle, Szintillationsdetektor und schreibendem Meßgerät, verwendet 1.     

Phase Transition of [2,2]‐Paracyclophane – An End to an Apparently Endless Story

In this contribution, the solid‐state low‐temperature phase structure of [2,2]‐paracyclophane is unambiguously characterised by single‐crystal X‐ray analysis. Additionally, a heat capacity measurement was undertaken, which proves the existence of a λ‐type phase transition at 45 K, a transition that is connected with the formation of a secondary C_p/T feature at 60 K. The low‐temperature phase (<45 K) crystallises in the lower symmetry space group P$\bar 4$ n2, whereas the high‐temperature phase (>60 K) crystallises in space group P4₂/mnm. This proves what has been postulated both by experimental and theoretical chemists but has repeatedly been dismissed as speculation many times.     

Synthesis and Structure of K[Cd(O2N‐C6H4‐NNN‐C6H4‐NO2)3], an Anionic 1, 3‐Bis(4‐nitrophenyl)triazenido Complex of Cadmium

The reaction of cadmium acetate in methanol with 1, 3‐bis(4‐nitrophenyl)triazene in THF in the presence of KOH yields K[Cd(O₂NC₆H₄NNNC₆H₄NO₂)₃] in form of hexagonal prismatic, red crystals with the trigonal space group R3¯ and a = 12.229(2), c = 48.988(10) Å and Z = 6. In the anionic cadmium complexes, which are located along the threefold axis, the Cd atoms are coordinated in a trigonal prismatic arrangement by the atoms N(1) and N(3) of three triazenido ligands. The potassium cations are coordinated icosahedrally by oxygen atoms of each one nitro group of six neighbouring anionic complexes. The Cd‐N distances are 2.376(4) and 2.350(4) Å, and the K‐O distances are in the range of 2.833(6) to 3.365(6) Å.     

Reaction of N‐Heterocyclic Silylenes with Thioketone: Formation of Silicon–Sulfur Three (Si‐C‐S)‐ and Five (Si‐C‐C‐C‐S)‐Membered Ring Systems

Three‐ and five‐membered rings that bear the (Si‐C‐S ) and (Si‐C‐C‐C‐S ) unit have been synthesized by the reactions of L SiCl ( 1 ; L =PhC(NtBu)₂) and L′ Si ( 2 ; L′ =CH{(C?CH₂)(CMe)(2,6‐iPr₂C₆H₃N)₂}) with the thioketone 4,4′‐bis(dimethylamino)thiobenzophenone. Treatment of 4,4′‐bis(dimethylamino)thiobenzophenone with L SiCl at room temperature furnished the [1+2]‐cycloaddition product silathiacyclopropane 3 . However, reaction of 4,4′‐bis(dimethylamino)thiobenzophenone with L′ Si at low temperature afforded a [1+4]‐cycloaddition to yield the five‐membered ring product 4 . Compounds 3 and 4 were characterized by NMR spectroscopy, EIMS, and elemental analysis. The molecular structures of 3 and 4 were unambiguously established by single‐crystal X‐ray structural analysis. The room‐temperature reaction of 4,4′‐bis(dimethylamino)thiobenzophenone with L′ Si resulted in products 4 and 5 , in which 4 is the dearomatized product and 5 is formed under the 1,3‐migration of a hydrogen atom from the aromatic phenyl ring to the carbon atom of the C? S unit. Furthermore, the optimized structures of probable products were investigated by using DFT calculations.